High-gain antennas for millimeter-wave (MMW) applications may be designed in the various forms such as non-planar (e.g. array of openings (slots) in a side wall of a waveguide or horn antennas) or planar antennas (e.g. an array of periodic printed patches or slots).
A non-planar (e.g. horn) antenna may provide a high radiation gain, at the expense of its size. The horn antenna may be difficult to integrate with other planar sub-systems due to size constraints. To achieve the same maximum gain, the horn antenna's dimensions decreases as frequency of operation is increased; this adds complication to the fabrication process since connectors of the antenna require high precision machining which is very expensive. Also, the excitation of non-planar antennas (e.g. horn antennas) becomes challenging at high frequencies.
Considering planar antennas, to achieve high radiation gain, an array of microstrip or slot antennas printed on a planar substrate may be used. For planar array antennas, each element must be fed separately. One drawback of such antennas is designing and tuning the complex feeding network. To limit the associated losses of a feeding network, a low-loss substrate should be used which may be expensive.
Low-loss substrates for printed structures operating at MMW frequencies, such as 60 GHz and above, are very expensive, and the feed network to excite such a large array (in order to provide high radiation gain) is bulky, thereby increasing the overall size of the array, dielectric loss, and ohmic loss.
Therefore, there is a need for a planar antenna that may be integrated with and fabricated as part of PCB, while overcoming the aforementioned drawbacks and shortcomings.